Because of the thin walls I increased the number of vertical walls and solid layers to add strength. In the photo version I added the model D&D Keychain as a part to the lid, and used the painter to add color to the logo since I have the MMU.
The author remixed this model.
I scaled the size to fit two stacks of the cards and added a divider. I also separated the box and lid into two objects vice one to allow editing and manipulation.